Arnold-Chiari syndrome is a form of malformation that is caused due to the structural defects within the human brain and the spinal cord. These defects are seen during the process of foetal development.
The bony space that becomes indented at the lower portion of the skull is extremely small, and this is due to the ancestral changes or a maternal food regimen that lacks certain nutrients. As a result, the pressure is more on the cerebellum. Quite importantly, this in turn hinders cerebrospinal fluid's flowing movement, resulting in the protection and the encapsulation of the brain and the spinal cord, like a soft cushion. It mainly occurs in the foetal state, but at the same time, Chiari malformations are also seen less commonly during the later stages of one's life. This occurs when excessive levels of cerebrospinal fluid becomes drained away due to reasons such as injury, infection, and also as a result of exposure to poisonous substances.
Based on the cause of the malformation, there are three kinds of Chiari malformations.
Type I Chiari malformation is the least serious form where the lowest part pertaining to the hind portion of the brain, also called as the cerebellar tonsils, drops towards the top portion of the spinal canal. Generally, the lower parts of the brain exist in a space within the skull, which is located above the region called foramen magnum. This is at the opening of the skull base. In Type I Chiari malformation, such brain parts get pushed downwards since they become too big for the skull. When these brain parts are pushed out from the skull towards the region of spinal cord, this exerts pressure towards the base of the brain. It also blocks the flow of cerebrospinal fluid (CSF), to and from the brain.
The less common types are Type II and III Chiari malformations. Type II is associated with a condition called Spina bifida. Spina bifida is a birth defect associated with spine development and it occurs in adults who suffer from hydrocephalus, where the fluid builds up in the brain.
Type II is also called as the classic form of Chiari malformation, involving extension of both the brain stem and the cerebellum towards foramen magnum.
Type III involves the protrusion of the cerebellum portion, as well as the brain stem, and leads to severe neurological defects. This is a relatively rare form compared to Type II.
Type IV is characterised by undeveloped cerebellum and may be associated with exposed regions of the skull, as well as the spinal cord.
Chiari malformations are also caused due to syringomyelia, a disorder involving cyst development in the central canal of the spinal cord and the spinal curvature called scoliosis (characterised by the bending of the spine towards the left or right) and kyphosis (involves bending of the spine in a forward axis).
Chiari malformation is also seen running in families, and few children born with the disorder may be carrying a faulty gene that would have caused problems regarding skull development in the womb. At the same time, the risk of a parent passing Chiari malformation to the child is very small, and even in case they inherit it, there may not be any symptoms.